json_arrindex

THE RISK

Low Risk

Why json_arrindex needs a policy

This is a pure read operation that queries array data to locate a value's position. It has no ability to modify state, execute commands, or affect resources. The blast radius of misuse is minimal—worst case returns incorrect index information. Confidence is high despite the generic tool name because the description clearly indicates a read-only lookup function.

From the tool's definition Tool description states 'Get the index of value in array at path' - a retrieval operation with no side effects. Returns positional information from existing data structures without modification, creation, or deletion.

Documented attack patterns abuse exactly the kind of access json_arrindex gives an agent:

POLICY

How to control json_arrindex

PolicyLayer is an MCP gateway — it sits between your AI agents and Amazon ECS MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for json_arrindex:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "json_arrindex": {}
  }
}

json_arrindex is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.

Create a free account and register Amazon ECS MCP Server — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

CAP THIS TOOL →

Free to start. No card required.

EXPLORE

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Go deeper

Roll out MCP under one policy → Per-person scoped tokens, one central policy, and full audit across every server your team connects.
The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Data exfiltration → How read access becomes an exfiltration channel when chained with untrusted content.
MCP token cost → What connecting this server costs in context-window tokens on every request.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →
PolicyLayer vs alternatives → How deterministic, per-call MCP policy compares with gateways, identity layers, and authorisation platforms.

FAQ

Questions about json_arrindex

What does the json_arrindex tool do? +

Get the index of value in array at path. It is categorised as a Read tool in the Amazon ECS MCP Server MCP Server, which means it retrieves data without modifying state.

How do I enforce a policy on json_arrindex? +

Register the Amazon ECS MCP Server MCP server in PolicyLayer and add a rule for json_arrindex: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Amazon ECS MCP Server. Nothing to install.

What risk level is json_arrindex? +

json_arrindex is a Read tool with low risk. Read-only tools are generally safe to allow by default.

Can I rate-limit json_arrindex? +

Yes. Add a rate_limit block to the json_arrindex rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.

How do I block json_arrindex completely? +

Set action: deny in the PolicyLayer policy for json_arrindex. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.

What MCP server provides json_arrindex? +

json_arrindex is provided by the Amazon ECS MCP Server MCP server (awslabs.ecs-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Amazon ECS MCP Server tool call.

Start from Amazon ECS MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →